Recording information onto optical disks is performed by modulating light intensity and forming recording marks on the media. To do this, a coding scheme and circuit to record digital signals onto the recording media are required. In general, run length limited coding has been used. In the run length coding rule (RLL constraints), information is recorded by NRZI modulation coding in which pulse polarity is inverted only when a “1” bit of code is encountered and information can be stored on both edges of a recording mark, namely, edge mark recording.
After coding original data incoming from the host, the coded data includes DC components because the time width of one polarity pulses is longer than that of the other polarity pulses. Because these DC components cause jitter to increase and errors, it is desirable to minimize the DC components.
To address this, there have been proposed techniques for making the Digital Sum Value (DSV) of a recording bit stream as close to zero as possible, a few of which will be cited below. A technique disclosed in JP-A No. 272726/1987 (patent document 1) inserts two types of sync signals into data to reduce the DC components and uses these two signals appropriately to set pulse polarity inversed or not inversed just before the next sync signal.
A technique disclosed in JP-A No. 225709/1993 (patent document 2) incorporates a plurality of resync signal patterns at given intervals in recording bit stream signals, one of these patterns having an odd number of polarity reversals and the other having an even number of polarity reversals, and selects a pattern appropriate for a recording data pattern to reduce the DSV.
A technique disclosed in JP-A No. 177430/1999 (patent document 3) divides a bit stream into segments and calculates the DSVs of the segments. This technique carries out DSV control by comparing the DSV of a new segment with the total DSV of the previous segments and determining whether or not to invert the polarity of the bits in the segment.
In order to increase the number of cycles allowed for repetitive writing on disk, for example, JP-A No. 197662/2002 discloses a polarity inversion technique for DVD-RAM disks, that is, this technique randomly inverts the mark and space positions each time rewriting is performed. RLL 8-16 modulation that is used for DVDs encodes user data in edge positions. Therefore, because of edge recording, information is recorded in both marks (amorphous) and spaces (crystalline) of a pattern recorded on the disk. Taking advantage of the 8-16 modulation characteristics and data area separated into sectors, DVD rewritable lifespan is enhanced by randomly placing a mark or space in the beginning position of each sector to prevent only marks (or spaces) from being present in fixed positions of recorded patterns. This is called a polarity inversion method.
Using various techniques as above, rewritable DVDs satisfy the required number of cycles: not less than 1,000 for DVD-RW and not less than 100,000 for DVD-RAM.
[Patent Document 1] JP-A No. 272726/1987
[Patent Document 2] JP-A No. 225709/1993
[Patent Document 3] JP-A No. 177430/1999
[Patent Document 4] JP-A No. 197662/2002